Various personal computers, such as, but not limited to, a desktop type, a tower type and a notebook type personal computer, have been developed and marketed with a recent advance of technology. Among them, the notebook computer is a battery driven type personal computer designed to provide a portability feature.
The notebook computer does not generally contain extra space for mounting a peripheral apparatus, since a compact size and light weight features are important. In some cases, the expansion of devices cannot be realized by a PC card. Also, the number of bus slots is remarkably limited since the available surface area is small. Desktop computers are usually provided with more than 10 bus slots, while most of the laptop/notebook type computers are not provided with bus slot capability, and only some are provided with one or two bus slot(s). The notebook computer is characterized in that it is easily carried, and accordingly it is troublesome to connect various cables, such as a printer cable, a monitor cable, a communication cable, etc., to the notebook computer when the notebook computer is used in an office, and to disconnect the cables when the notebook computer is carried. This aspect causes usability to be decreased.
The expansion unit provides the notebook computer with the same working environment as that of the desktop computer without affecting the portability when the notebook computer is used in the office. The main functions of a docking station include a port replication function and a bus expansion function.
The port replication function is realized by an expansion unit which is provided with a plurality of extended lines of the port signals of the notebook computer. If a printer, a CRT display, an external keyboard, etc. are connected to each of the ports of the expansion unit in advance, the user can immediately use the printer, the CRT display, the external keyboard by placing the notebook computer onto the expansion unit. If the connection of the these external equipments to the expansion unit is maintained, these external equipments can be immediately used by another user connecting their notebook computer to the expansion unit, whereby each user is released from the troubles and work of connecting or disconnecting the various cables. It is sometimes referred to as a cable management function since the management of the connection of the cables is necessarily accomplished at one time.
The bus expansion function is realized by providing the expansion unit with the extended portions of the bus of the notebook computer, such as a PCI (Peripheral Component Interface) bus as a local bus, and an ISA (Industry Standard Architecture) bus as a system bus. The expansion unit has a space (media bay) for receiving an external memory device connected to the bus, and bus slots for mounting adapter cards. It is possible to provide the notebook computer with a file subsystem or a network subsystem by connecting a hard disk drive (HDD), a SCSI (Small Computer System Interface) card, and a LAN adapter to the expansion unit in advance.
Sometime, the expansion unit is referred to as the docking station. Also, the expansion unit having only the port replication function is referred to as a port replicator. The expansion unit itself is disclosed in a Japanese patent application specification H05-181593 and U.S. Pat. No. 5,555,487.
The supply of power to the electric/electronic apparatus is usually made by converting an AC voltage of a commercial power source to a DC voltage by an AC adapter, and distributing the DC voltage to each section of the apparatus after converting and stabilizing the DC voltage by a DC/DC converter.
In the case of the above described notebook computer, the DC/DC converter is built into the computer, and the AC adapter is located outside of the computer. The cost, size and weight of the power supply circuit, such as the AC adapter and the DC/DC converter, tend to increase in order to meet a required power capacity. Accordingly, the power capacity of this power supply circuit is designed to meet a power requirement in an actual use environment.
The power supply system used in the case to which the notebook computer is mounted to the expansion unit is classified as a first system in which the DC power from the AC adapter mounted on the computer side is commonly used by the computer and the expansion unit, and as a second system in which the DC power from the AC adapter mounted on the expansion unit side is commonly used by the computer and the expansion unit. If the expansion unit is of the port replicator type, the power consumption of the expansion unit side is relatively small since the expansion unit contains only the low power consumption type apparatus, such as the external keyboard/mouse, and the self powered apparatus, such as the CRT display, the printer, etc., which is provided with their power supply circuit.
Accordingly, for the first system, the system can be used in which the DC power of the standard power capacity generated by the AC adapter mounted in the notebook computer is supplied to all the components. If the expansion unit is of the docking station type, the power consumption of the expansion unit side becomes large as a result of the fact that many peripheral equipments are connected to the expansion unit. In this case, since it is expected that the remarkably large power consumption exceeds the power consumption in the actual use environment of the notebook computer, it is considered preferable to use the second type of system in which the power supply is prepared in the expansion unit side rather than to increase the power capacity of the standard AC adapter designed to be used in the actual use environment of the notebook computer.
The computer system is provided with so called open slots, such as the bus slots and the PC card slots into which a card with various power capacity is inserted. Although the electric and mechanical specifications of the adapter card inserted into the bus slot and the PC card inserted into the PC card slot are defined, the power capacity of the cards are not defined in most cases. For example, an Ethernet card, a wireless LAN card, the HDD, a PC card for ZV port, etc., are driven by a relatively large current. In the case that the apparatuses requiring the large current are simultaneously connected to the open slots of each of the computer and the expansion unit, the remarkably large power capacity exceeds the power capacity in the actual use environment of the notebook computer defined by a manufacturer for the design and the fabrication required.
An approach made as a relatively simple method for resolving the shortage of the power capacity, is one in which the AC adapter and the DC/DC converter are designed and fabricated to have a certain margin. However, recently notebook computers have been equipped with the external memory devices, such as the HDD, CD-ROM drive (or DVD drive), FDD, so that the power requirement of the notebook computer in their actual use environment has been increased. For example, a notebook computer equipped with the AC adapter of the power capacity exceeding 50 W has been marketed. Accordingly, the cases in which the problem is not solved by the simple approach of increasing the power capacity of the power supply circuit have been increased. Attaching the large capacity power supply circuit to the notebook computer as the standard option for an environment in which the connection of the apparatus requiring the large power is expected, causes a disadvantage in view of the product costs. The portability of the notebook computer is also sacrificed since the size of the power supply circuit becomes large.
In this related environment, ZV (Zoom Video) is a standard having a connecting compatibility with the PC card. The PC card for the ZV port realizes a high speed display of motion picture by performing a direct transfer of the data to and from a video controller.